Table IX. Comparisons of Committed Effective Dose Equivalent Detection Limits

DOE-STD-1121-98

more precise, even if far less accurate. Finally, for short-lived radionuclides (e.g., the decay products of

radon), there may not be any bioassay procedure; the only available methods involve air monitoring.

Precision refers to how reproducible a measurement is. Bias or accuracy refers to how close the

average of measurements is to a "conventionally true value." Precision and bias are independent, that is,

measurements may be biased or unbiased without regard to their precision, and they may be precise or

imprecise without regard to their bias.

Sensitivity, as used here, refers to the lowest HE,50 that can be distinguished from background.

Technology shortfall, as defined in the DOE Internal Dosimetry Program Guide (DOE 1999b), occurs

when the sensitivity of a dose assessment method is not adequate to meet the dose assessment

requirements of 10 CFR 835.

The best accuracy and precision for HE,50 assessment in the DOE is that for intakes of tritium when

assessments are based on urinalysis bioassay results. Doses can be assessed to within 10% to 20% after

only a couple of measurements over a couple of days. Even a site with a detection limit of 0.01 :Ci of 3H

per liter of urine (10,000 pCi/L) can detect 0.04 mrem immediately after a tritium intake, and 22 mrem 90

days after a tritium intake. With an average tritium sampling frequency of every 14 days, one can detect a

committed effective dose equivalent of 0.1 mrem, or about 1000 times less than the level at which a

bioassay program is required by 10 CFR 835. Two cases are shown in Table IX, for effective clearance

halftimes of 10 days (Reference Man) and 7 days (typical of a summer day). Dose numbers are higher for

effective clearance half-times shorter than 10 days. Thus, for tritium, accuracy, precision, and sensitivity

are no problem.

Table IX. Comparisons of Committed Effective Dose Equivalent Detection Limits for Tritium

Bioassay When 0.01 :Ci/L of 3H Is Observed, as a Function of Time since Intake

HE,50 Inferred from 0.01 :Ci/L of 3H in urine (mrem)

Teff = 10 days

Days Since Intake

Teff = 7 days

0.04

0.03

0.11

0.47

220

In the DOE, the worst accuracy for HE,50 assessments occurs for plutonium and actinides based on air

monitoring data and worker's stay time. Such measurements, however, may result in assessed doses that

are both more precise and far more sensitive than doses assessed on the basis of bioassay measurements.

In the case of plutonium, there is a technology shortfall for doses assessed on the basis of routine

urinalysis bioassay; such programs have such poor sensitivity that they may miss doses of several rems

(thousands of millirems). Continuous air monitors for plutonium can readily detect 10 to 30 DAC-h under

field conditions, corresponding to HE,50 values of 25 to 75 mrem. Lapel air samplers, for which air filters

are measured in the laboratory, can do somewhat better.

Short-lived decay products of 222Rn are found where there are radium-bearing residues of uranium

ores. There is no practical method of bioassay for such decay products, so the only alternative is to use

air monitoring results.

The results of the comparison of these three cases are shown in Table X.